Add complete time series aggregation example and refactor OKXCollector for repository pattern

- Introduced `example_complete_series_aggregation.py` to demonstrate time series aggregation, emitting candles even when no trades occur.
- Implemented `CompleteSeriesProcessor` extending `RealTimeCandleProcessor` to handle time-based candle emission and empty candle creation.
- Refactored `OKXCollector` to utilize the new repository pattern for database operations, enhancing modularity and maintainability.
- Updated database operations to centralize data handling through `DatabaseOperations`, improving error handling and logging.
- Enhanced documentation to include details on the new aggregation example and repository pattern implementation, ensuring clarity for users.

tests/test_real_storage.py

@@ -14,7 +14,7 @@ from datetime import datetime, timezone
 
 from data.exchanges.okx import OKXCollector
 from data.base_collector import DataType
-from database.connection import DatabaseConnection
+from database.operations import get_database_operations
 from utils.logger import get_logger
 
 # Global test state
@@ -36,12 +36,15 @@ signal.signal(signal.SIGTERM, signal_handler)
 async def check_database_connection():
     """Check if database connection is available."""
     try:
-        db_manager = DatabaseConnection()
-        # Test connection
-        with db_manager.get_session() as session:
-            session.execute("SELECT 1")
-        print("✅ Database connection successful")
-        return True
+        db_operations = get_database_operations()
+        # Test connection using the new repository pattern
+        is_healthy = db_operations.health_check()
+        if is_healthy:
+            print("✅ Database connection successful")
+            return True
+        else:
+            print("❌ Database health check failed")
+            return False
     except Exception as e:
         print(f"❌ Database connection failed: {e}")
         print("   Make sure your database is running and configured correctly")
@@ -49,18 +52,22 @@ async def check_database_connection():
 
 
 async def count_stored_data():
-    """Count raw trades and candles in database."""
+    """Count raw trades and candles in database using repository pattern."""
     try:
-        db_manager = DatabaseConnection()
-        with db_manager.get_session() as session:
-            # Count raw trades
-            raw_count = session.execute("SELECT COUNT(*) FROM raw_trades WHERE exchange = 'okx'").scalar()
-            
-            # Count market data candles
-            candle_count = session.execute("SELECT COUNT(*) FROM market_data WHERE exchange = 'okx'").scalar()
-            
-            print(f"📊 Database counts: Raw trades: {raw_count}, Candles: {candle_count}")
-            return raw_count, candle_count
+        db_operations = get_database_operations()
+        
+        # Get database statistics using the new operations module
+        stats = db_operations.get_stats()
+        
+        if 'error' in stats:
+            print(f"❌ Error getting database stats: {stats['error']}")
+            return 0, 0
+        
+        raw_count = stats.get('raw_trade_count', 0)
+        candle_count = stats.get('candle_count', 0)
+        
+        print(f"📊 Database counts: Raw trades: {raw_count}, Candles: {candle_count}")
+        return raw_count, candle_count
     except Exception as e:
         print(f"❌ Error counting database records: {e}")
         return 0, 0